Plant breeders have altered through genetics the starch, protein and oil content of corn to better meet the needs of the livestock feeder, the food industry, and other industrial users of corn. As a result of their modifications of ordinary dent types, new specialty corns have been created, including WAXY, HIGH-AMYLOSE, HIGH OIL, and HIGH-LYSINE corn. Specialty corn hybrids are not grown as widely as ordinary dent corn and their availability and adaptability to certain areas may be limited. The following provides information on the management and utilization of specialty corn hybrids.
WAXY CORN is a starch variant of normal corn. Waxy corn contains 100 percent amylopectin whereas normal corn contains 75 percent amylopectin and 25 percent amylose. Amylopectin is a form of starch which consists of branched glucose subunits whereas amylose is made up of unbranched glucose molecules. Waxy corn is not new; it was found in China in 1908. The waxy trait is controlled by a single recessive gene, the wx gene.
Waxy corn is used by wet-corn millers to produce waxy cornstarch which is utilized by the food industry as a stabilizer/thickener and in the paper industry as an adhesive. Waxy corn for wet milling is usually grown under contract for wet-corn millers or exporters.
HIGH-AMYLOSE CORN - Amylomaize is the generic name for corn that has an amylose content higher than 50%. High-amylose corn is grown exclusively for wet-milling. The starch from high-amylose is used in textiles, candies and adhesives.
HIGH-OIL corn contains approximately 7 to 8 percent oil. This is a 2 to 3 percent increase over normal corn. Additionally, protein quality and quantity are increased somewhat in high-oil corn. This is because the germ size is larger and it contains protein of higher quality than the endosperm. The high-oil trait is controlled by many genes and is derived from the Illinois High-Oil selection program.
HIGH-LYSINE corn contains increased levels of two amino acids--lysine and tryptophane--which are essential in the diets of nonruminants. Both of these amino acids are nutritionally limiting in normal corn. This protein alteration is controlled by a single recessive gene, Opaque-2, which was discovered in 1964.
Production practices for producing maximum grain yield using waxy, high-amylose, high-oil, and high-lysine hybrids are similar to those for normal grain hybrids. That is, good fertility, adequate weed control, proper planting date, etc., are necessary to produce maximum yields. However, there are certain characteristics of specialty corns which warrant consideration. Care must be taken to avoid cross pollination with normal hybrids. If cross pollination occurs, the cross-pollinated ears of the waxy, high-amylose and high-lysine hybrids will produce normal seed and the seed of the high-oil hybrid will have an oil percentage intermediate between the normal and high-oil hybrid. Corn grown under contract is usually checked for possible contamination with field corn. To avoid cross pollination, specialty hybrids should be grown in an isolated field or the grain from the border six to ten rows should be harvested separately from the rest of the field. Additionally, these specialty hybrids should be grown following crops other than corn to avoid volunteer corn.
Proper hybrid selection of specialty corn types is complicated by the lack of entries in the Ohio Corn Performance Test. Both high-lysine and waxy hybrids have been entered in past years but there is no performance data available for high-amylose and high- oil types.
The potential grain yields of specialty corn hybrids are generally lower than those of dent corn hybrids. Newer waxy hybrids are reported to be more competitive with dents in yield. High-amylose corn yields vary depending upon location but average 65 to 75% of ordinary dents. Insufficient yield data are available for high-oil hybrids to decide the trade-off, if any, between grain yield and high-oil content. Limited data do indicate that high-oil type hybrids containing 7 to 8 percent oil may be produced with little or no sacrifice in yield.
Grain yields of high-lysine hybrids averaged 13 to 19% less than those of normal dent hybrids in state corn trials conducted over a 4-year period in the 1970's. The lysine content in grain of opaque-2 hybrids ranged from 0.34 to 0.37% compared to 0.26 to 0.30% for normal dent types. More recent evaluations of high- lysine corn performance indicate that yield potential has been improved but that yields are still about 7 to 10% lower than normal dent corn counterparts. The opaque-2 gene is characterized by a soft, chalky endosperm which has resulted in greater susceptibility to ear and kernel rots in certain genetic backgrounds. However, modifications have been made to improve kernel quality and resistance to breakage. Test weight can also be lower with high- lysine corn than normal dent hybrids so care must be taken to select a hybrid with adequate test weight.
Feeding trials have been conducted with waxy, high-oil, and high- lysine corn. The results from a considerable number of waxy corn feeding trials on all types of livestock have been inconsistent. While a few of the trials showed statistically significant increases in rate of gain and/or feed efficiency, most trials showed only slight positive changes or no changes. A conservative approach would be to grow waxy hybrids for feed purposes only if they yield equal to or greater than normal hybrids.
High-lysine hybrids have demonstrated nutritional advantages over normal corn. The nutritional advantage is only for nonruminants, such as swine, since the microflora in the rumen of ruminants can synthesize lysine and tryptophane. The value of high-lysine corn in poultry rations is limited by a third amino acid - methionine. The methionine content of high-lysine corn is adequate for swine but not for poultry.
Feeding trials with high-oil corn indicate improved feed efficiency and rate of gain. This is expected since oil contains more energy per pound than starch.
Prepared by:
Peter Thomison
Extension Agronomist
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